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234

ORDINARY BRONZES

2.  Determination  of the  Antimony.—The   filter-paper  with   the
antimony sulphide is heated in a beaker with 4 c.c. of 50% sodium hydroxide
solution and 20-30 c.c. of sodium sulphide (D = 1-225) until the antimony
sulphide is completely dissolved.   After some time the liquid is filtered
directly into the Classen dish, the vessel and filter being washed with 50-60
c.c. of sodium sulphide.   The filtrate is treated with 5-6 grams of potassium
cyanide to decolorise the sodium sulphide and to prevent formation of
polysulphides during the electrolysis, which is carried out at the ordinary
temperature.   Cathode, Classen capsule;   anode, disc or   spiral;   ND100
= 0-15-0-18  arr.p.;   voltage = 1-1-2 ;   duration   (0-1-0-15   gram   Sb) =
15-18 hours.

When the antimony is all deposited, the anode is withdrawn, the cap-
sule rapidly emptied, washed with water, alcohol and ether, and dried at

70°.

The antimony is afterwards removed from the dish by treatment with
nitric acid (D 1-2) containing a little tartaric acid in solution.

3.  Determination of the Copper, Lead, Iron and Zinc.—The liquid
from which the metastannic acid was separated (see i) is acidified with
15-20 c.c. of nitric acid (D 1-2), mixed with the nitric acid solution of the
oxides extracted from the metastannic acid and the. whole treated as in the
analysis of ordinary brass (q.v.).

4.  Determination of the Nickel.—See Nickel Bronzes.

5.  Determination of the Manganese.—See Manganese Bronzes.

6.  Determination of the Silver.—5-10  grams  of the sample are
treated with nitric acid and freed from metastannic acid in the ordinary
way.    In the filtrate the silver is precipitated with hydrochloric acid by
the procedure followed for the determination of silver in copper.1

7.  Determination of the Phosphorus.—See Phosphor Bronzes.

8.  Determination of the Arsenic.—See Copper.

9.  Determination of  the Sulphur. —2   grams   of   the   sample   are
treated with nitric acid and the stannic acid separated as usual.    From
the filtrate the copper is eliminated by electrolysis in nitric acid solution,
the residual liquid being evaporated to dryness and the sulphur then deter-
mined as in copper (q.v.).

B.   Gravimetric Method

1. Determination of the Tin.—In a covered beaker, 1-2 grams of
the alloy as filings are treated with 15-20 c.c. of nitric acid (D 1-3), the
metastannic acid being separated, washed, ignited in a porcelain crucible
and weighed: Sn02 x 0-7881 = Sn. The filtrate is treated as in 3.

The stannic oxide thus weighed is always impure and, where an exact
determination is necessary, it is powdered in an agate mortar, mixed with
6 parts of a mixture of ignited sodium carbonate and sulphur in equal pro-
portions, and heated at a gentle heat with the crucible covered until all the
sulphur is expelled.

1 Since silver is deposited with the copper on the cathode, the data relating to
copper must be corrected by the amount found.and ether, and dried at 70°.